The long term objective of this study is to determine what extragenetic factors the spermatozoon provides the ovum at fertilization. The mitochondrial microinjection technique we have developed will be used to define the role of paternal mitochondria during fertilization and early embryogenesis. A transgenic approach will be taken to elucidate why testicular mitochondria require a novel isozymic variant of the mitochondrial oxidative phosphorylation protein cytochrome c. DNA sequence and hybridiza- tion studies will be conducted to determine whether the mitochondria of the spermatozoon are programmed for non- proliferation and gossypol will be used as a molecular probe to investigate mitochondrial differentiation in the mammalian testis. These studies will help identify epigenetic and nuclear regulated processes that are essential for normal mammalian development. A better understanding of these events is necessary to explain how perturbations lead to birth defects. In addition, a more detailed comprehension of the biochemical events at and following fertilization will provide necessary information to aid in the treatment of the infertile and may provide superior approaches to fertility control.